Compressional wave translating device



ago 33, fiwfi. '3 pgpg COMPRESSIONAL WAVE TBANSLATING DEVICE Filed March 13, 1943 INVENTOR 7..4 POPE 8 04m 6, M

ATTORNE? Patented Aug. 13, 1946 COMPRESSIONAL WAVE TRAN SLATIN G DEVICE Thomas J. Pope, East Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 13, 1943, Serial No. 479,084

9 Claims.

This invention relates to compressional wave translating device and more particularly to microphones specially suitable for use in supersonic submarine signalin systems.

One object of this invention is to obtain a predetermined directional characteristic for sonic translating devices. More particularly, one object of this invention is to realize from a supersonic hydrophone an output the directivity pattern of the magnitude of which is accurately indicative of the direction of the source of the supersonic waves with respect to the hydrophone.

In one illustrative embodiment of this invention, a hydrophone comprises a group of compressional wave responsive elements associated with a common diaphragm, the elements individually having predetermined directional response characteristics, and means for combining the outputs of the several elements to produce a desired directional characteristic for the group of elements. In a particular construction, the several elements are formed of multi-slab piezoelectric crystals, the crystal slabs of each element being oriented mechanically and electrically to operate cophasically.

In accordance with one feature of this invention, the group of wave responsive elements comprises a central non-directional element and two two-part bidirectional elements having substantially cosine directivity, the parts of the bidirectional elements being arranged in quadrature about the central element and the two Darts of each bidirectional element being diagonally opposite one another. The central element is electrically associated with the bidirectional elements in such manner that the response pattern of the group of elements is composed of four cardioidal lobes orthogonally related.

The invention and the above noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. 1 is an elevational view mainly in section of a supersonic hydrophone illustrative of one embodiment of the invention;

Fig. 2 is in part a sectional view of the hydrophone, taken along plane 2-2 of Fig. 1 and in part a circuit diagram illustrating one manner of utilizing the hydrophone Fig. 3 is a diagram showing the directional response characteristic of the hydrophone illustrated in Figs. 1 and 2; and

Fig. 4 is a diagram illustrating the cooperation of the translating elements in the device shown in Figs. 1 and 2 to produce the directional pattern illustrated in Fig. 3.

Referring now to the drawing, the hydrophone shown in Figs. 1 and 2 comprises a cylindrical housing I 0, for example of metal, having an apertured end portion I I, the aperture in this portion being closed by a diaphragm I2, for example of rubber, joined or secured in water tight relation to the housing. Within the housing and seated upon and secured to an internal shoulder I3 is a cylindrical metallic, for example steel or lead, or ceramic support or plate I4 upon which a group of translating units of the hydrophone is mounted.

This group includes, as shown in Fig. 2, a central element I5, and four similar outer elements Illa, IBb, I'Ia and Nb disposed about the central element. The central element I5 is of square form as shown and is composed of a plurality, for example four, of similar piezoelectric crystals such, for example, as 45 degree Y-cut Rochelle salt blocks or slabs, mounted in face to face relation. The several blocks or slabs are physically oriented and electrically interconnected in parallel in known manner so that all respond electrically in the same Way in response to pressure variations therein, that is, so that the electromotive force generated in each block or slab when it is subjected to pressure in the direction of the end faces thereof is in the same direction and in phase with that generated in the other blocks or slabs.

Each of the outer elements I Go, I Eh, I la and I'll) is L-shaped and, like the central element, is composed of piezoelectric, e. g., 45 degree Y-cut Rochelle salt, crystal blocks or slabs physically oriented and electrically interconnected in such manner that the blocks or slabs react in the same way to pressure variations therein. Further, diagonally opposite outer elements are connected electrically in series or parallel opposing so that,

in eiTect, the hydrophone comprises two bi-Dart translating elements, IBa, I61) and Ila, I lb, orthogonally related and symmetrically arranged with respect to the central element I5.

The several elements are secured to the plate I4 and insulated therefrom. For example, these elements may be joined to the plate by cementing to a relatively thin ceramic plate indicated at I9, having a low dielectric constant, this plate being in turn cemented to the plate I4. As shown in Fig. 1, all of the elements are of the same height, i. e., of the same dimension normal to the face of the plate I 4 to which they are secured. The end faces of the elements toward the diaphragm I2 may be in firm engagement frequency pick-up device, as for example in echo ranging underwater object locating systems, the dimension of the elements noted and the thickness of the plate I4 are madeequal to a quarter wave-length of the signal frequency, for the transmission of this frequency therethrough. Of course, because the velocities of propagation of compressional wave energy through the piezo electric crystals and the metal plate I4 are different, the absolute magnitude of the height of the crystal blocks or slabs and of the thickness of the plate I twill be, different. The quarter wavelength dimensioning of the elements and plate I4 provides a vibrational ant-inode at the plane of joinder between the translating elements and theplate M and thus assures efficient conversion by V the translating elements of compressional wave energy conveyed thereto by the diaphragm I-2.- If the hydrophone is intended for use as a band frequency device, the crystal height and plate thickness advantageously are made equal to a quarter wave-length of the mean frequency in the band to be translated.

The diagonally opposite elements IEa, I61) and Ila, I1 1) are spaced, center to center, a distance substantially equal to one-half wave-length of the operating frequency, if single frequency operationis intended, or to one-half wave-length of the mean frequency in the band to be translated where'band frequency operation is intended. .The central translating element l5, it will be appreciated, is essentially non-directional about the aXisnormal to the ends thereof; that is, this element is equally sensitive to compressional waves impinging upon the diaphragm substantially irrespective of the angular location of the source of the waves with respect to this element. Each of. the bi-part elements I611, I522 and IIa, I'Ib, however, because of the half wave-length spacing of the parts thereof and inasmuch as the two parts of eachelement are in series or parallel opposing relation is markedly directional, and has substantially cosine directiv-ity. That is, when the source of the compressional waves is along the normal bisector to the diagonal connecting the two parts, the pick-ups of the two parts. are substantially equal and inasmuch as these parts are in series or parallel opposing the net pick-up of the two parts is zero; when the source of the compressional waves is along the diagonal between the two parts in either direction along this diagonal, the net pick-up of the two parts is a maximum; when the source is along aline at an angle to the diagonal, the net pick-up of the two parts is proportional to the cosine of the angle between this line and the diagonal.

Specifically, referring to Fig. 4, if the sound source is at the point S1, 1. e., along the diagonal AA, which is the normal bisector of the diagonal B-B, the compressional waves will arrive at the parts Na and Nb of the element defined by these parts at the same time so that the voltages generated in these two parts are equal; and inphase. Inasmuch asthese parts are connected electrically in opposition, as pointed out heretofore, the net voltage obtained from these tWo parts is zero. Inasmuch as the parts Ilia and I6!) are spaced one-half wave-length apart, the compressional waves will reach the part I 6a one-half cycle after they arrive at the part I619. Thus, the voltage obtained from the bidirectional element I 6a, IE1) is a maximum. Similarly, if the sound source is at a point St on the diagonal AA, the net voltage obtained from the parts I.Ia and I'll) is zero and that obtained from the bidirectional element Ita, Itb is a maximum. If the sound source is along the diagonal B-B, the response of the element Ita, I6b is zero and that of the element IfIc, I'Ib is a maximum.

'If the sound source is at a point S3 along a line making an-angle of 01 with the diagonal AA,

; the voltage obtained from the bidirectional elemen-t Ila, I'Ib will be directly proportional to cos 02. Similarly, the voltage obtained from the bidirectional element Ilia, IBb will be proportional to cos 01.

As noted heretofore, the element I5 is substantially equally responsive to compressional waves incidentupon the diaphragm I2 at any angle so that the voltage obtained from this element is independent of the direction of the sound source with respect to the hydrophone. This voltage maybe represented asE. The voltage obtained from the bidirectional elements, then, are proportional to E cos 0i and E cos 02-, respectively. Hence, when the voltage obtained from the nondirectional element is combined With that obtained from each bidirectional element, each of the resultants is of the form E (1+cos 0) and the directional pattern .of each bidirectional element in combination with, the non-directional element comprises two cardioids symmetrically located on opposite sides of, the axis normal to the wave receiving face of the diaphragm I2 and along the diagonal AA or B-B for the respective bidirectional element. Thus, the group of elements is equivalent to four hydrophones with cardioid directional patterns, the four patterns being in space quadrature. The directional pattern of the hydrophone as a whole is illustrated in Fig. 3 wherein the four cardioidal lobes, represent the response, in relation to direction of the source of the wave picked up with respect to the hydrophone, of the group of translating elements. Specifically, in Fig. 3, the lobe. A represents the response of the non-directional ele-. ment I5 'plus that of the bi:-directional element Ifiq, Ifib, lobe B that of the element I5 minus element Ilia, I61), lobe C that of the element I5 plus element I-Iu, -I 11) and lobe D that of element I5 minuselement I'I-a, I'Ib. In each such addition a shift of phase of the response. of the nondirectional element relative to that of the bidirectional element .is involved.

The outputs of the several elements. can. be combined, therefore, to produce an indication of the directional location of the source of the wave with respect to the hydrophone. For example, the translating elements may be connected by way of a resolving circuit, indicated at .20 inv Fig. 2., to thedeflectorplates E1. of a cathode ray oscillograph device 22 sothat the combined output of the elements is resolved into two crossed deflecting fields between the pairs of' defiector plates,the fields being related in. magnitude to. producea resultant effective to deflect the electron beam of. the device in the same direction as, the wave source bears with respect to the. hydrophone whereby the trace or, spot produced upon the screen of the oscillograph is a visual indication of the direction of the wave source with respect to the hydrophone.

. The general cooperative electrical association of the elements is illustrated in Fig. 2. As noted heretofore, the parts of each bi-directional translating element are connected in parallel or series opposing relation, as by conductors 25 and 26. The output of the non-directionalelement is combined with that of each bidirectional element and the two resulting voltages are supplied to the deflector plates 2 l. Specifically, the output of the non-directional element [5 is combined with that of the bidirectional elements [6a, l6b by way of the connections 28 and 29 and the resultant voltage is impressed be tween the deflector plates 2 la and 2 lb by way of the connections 30 and 3|. Similarly, the voltage impressed across the deflector plates Zlc and 2 Id by way of the connections 32 and 33 is the resultant of the outputs of element I5 and elements Ila, Ilb combined by way of the connections 34 and 35.

As shown in Fig. 1, pre-amplifiers 23 for the several translating elements may be mounted within the housing I0 and provided with a cable 24 leading from the housing through a watertight seal, not shown,

Although a specific embodiment of the invention has been shown and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. A compressional wave translating device comprising a central electromechanical translating element having a substantially non-directional response characteristic, two similar electromechanical translating elements having substantially cosine directivity, each of said two elements including two similar parts and the four parts of said two elements being arranged in alternate relation and space quadrature about said central element, means for electrically coupling aid central element to said two elements, and a diaphragm operatively associated with said central and two translating elements.

2. A compressional wave translating device comprising two similar bi-directional electromechanical translating elements having substantially coplanar active faces and similar cosine directional patterns orthogonally related in space, a substantially non-directional electromechanical translating element having its active face substantially coplanar with said active faces, means for electrically coupling said non-directional ele ment to said b-i-directional elements so that the response pattern of said bi-directional and nondirectional elements in combination includes four cardioidal lobes in space quadrature, and a diaphragm coupled to said active faces of said nondirectional and bi-directional elements.

3. A compressional wave translating device, two similar electromechanical translating elements each composed of two parts spaced a distance substantially equal to one-half wave-length of a preassigned frequency, the four parts of said elements being in space quadrature and the two parts of each element being diagonally opposite, a substantially non-directional electromechanical translating element centrally located with respect to said four parts, means for electrically coupling phragm cooperatively associated with said" two elements and said non-directional element.

4. A compressional wave translating device comprising two bi-directional electromechanical translating elements having predetermined similar directional characteristics, each of said elements including two L-shaped parts and the four parts of said elements being arranged to bound a square space, the two parts of each element being diagonally opposite, a central substantially nondirectionalelectromechanical translating element centrally located in said square space, means for electrically coupling said non-directional element to said bi-directional elements, and a diaphragm cooperatively associated with said non-directional and bi-directional elements.

5. A compressional wave translating device comprising two similar bi-directional electromechanical translating elements each of which includes two L-shaped parts spaced a distance substantially equal to one-half wave-length of a preassigned frequency, the four L-shaped parts being mounted in space quadrature with the arms of said L-shaped parts bounding a square space and the parts of each element diagonally opposite and electrically in opposition, a substantially non-directional electromechanical translating element mounted centrally in said space, means for electrically connecting said non-directional element with each of said .bi-directional elements to combine the outputs thereof, and means for driving all of said elements mechanically in commen.

6. A compressional wave translating device comprising support means, a piezoelectric crystal mounted on said support means and having a substantially non-directional response characteristic, a pair of bi-directional electromechanical translating elements each including two similar piezoelectric crystal parts mounted on said support means, the four parts of said elements being arranged symmetrically in space quadrature about said first crystal and the parts of each of said elements being opposite and electrically in series opposition, means for electrically connecting said first crystal to each of said elements, and a vibratory member operatively coupled to said first crystal and said elements.

'7. A compressional wave translating device comprising a support, an electromechanical translating element mounted on said support and having a substantially non-directional response characteristic, a plurality of piezoelectric crystals mounted on said support in symmetrical relation about said element and defining a pair of bi-directional translating elements having substantially cosine directivity, with the directional patterns of said two elements orthogonally related in space, means for mechanically driving said first element and crystals in common, and means electrically coupling said first element and each of said bi-directional elements to combine the electrical outputs thereof.

8. A compressional wave translating device comprising a support, a piezoelectric crystal mounted on said support and having a substantially non-directional response characteristic, two similar pairs of opposite similar piezoelectric crystals mounted on said support in quadrature about said first crystal, the crystals of each pair being spaced a distance substantially equal to one-half wave-length of a preassigned frequency and being connected electrically in opposition, means for mechanically driving all of said cryssaid last element to said two elements, and a diatals in common, and means for electrically conmeeting said: first crystal to each of said pairs of crystals'tocombine the electrical outputs thereof.

V :9. A supersonic hydrophone comprising a support, a substantially square piezoelectric crystal mounted on said support and having a substantially non-directional response characteristic, four L'-shaped piezoelectric crystals mounted on said support about said first crystal, each L- shaped crystal being opposite a corresponding corner of said first crystal andhavingits arms 10 8 parallel to tlie'a-djacent sides of saidifirst cry tal; diagonally opposite L-shapecl crystalsbeing spaced a distance substantially equal to one-half wave-length of a preassigned frequency and being electrically in series opposition, a diaphragm operatively coupled to all of said crystals, and means for combining the electrical output of said first crystal with that of each diagonally opposite pair of L-shaped crystals.

THOMAS J. POPE. 

